Message services is the term used to collectively identify the various office automation systems associated with a telephone switching system. These office automation systems are used to improve the productivity of the white collar worker in an office environment by providing an asynchronous voice (or short text message) communication medium.
The voice mail service system is one example of these message services. The voice mail service system offers two distinct communication features: Voice Mailbox (VM) and Call Answering (CA). The voice mailbox feature is involved when a message originator calls the voice mail service system by dialing an access code on the telephone station set touch-tone pad. The message originator identifies one or more message recipients who are also served by the telephone switching system by dialing their station numbers, and then generates a voice message for delivery by the voice mail service system to the designated message recipients. The delivery of the voice message may be immediate or at a scheduled time specified by the message originator. The delivery is passive in that the voice mail service system places the message in a mailbox assigned to each identified message recipient and activates the message recipient's message waiting indicator on the message recipient's telephone station set instead of actively calling the message recipient to playback the message. The message recipient may then access the voice mail service system to listen to the message, save the message for subsequent action, delete it, append comments and route the message to other message recipients, or reply and return a message to the message originator.
The call answering feature of voice mail service is geared to the convenience of the message recipient, unlike the voice mailbox feature which is geared towards aiding the message originator. The nonavailability of an individual to answer a telephone call results in that telephone call being redirected to the voice mail service system call answering feature. The caller receives a prerecorded announcement message from the absent individual and can then leave a voice message in the absent individual's voice mailbox.
The difficulty with existing voice mail service systems is that when a customer has a plurality of telephone switching systems with associated voice mail service systems, it is difficult to network the voice mail service systems together without incurring a significant transmission cost and a degradation of the quality of the voice transmission. The quality of the voice mail message transmission is a function of both the number of signal conversions and the quality of the transmission medium. A typical voice mail message system converts the received analog voice signal to digitally encoded form and stores this message in memory. The stored voice mail message is reconverted to analog form for transmission over standard voice-grade trunks to a distant voice mail system. The received analog voice mail message is reconverted into digitally encoded form and stored in memory in the distant voice mail system. The voice mail message remains in memory until the message recipient requests retrieval at which time the voice mail message is again converted to analog form and delivered to the message recipient.
Each analog-digital conversion operation negatively impacts on the voice quality of the voice mail message as well as uses expensive analog-digital signal conversion apparatus. In addition, the use of standard voice-grade trunks severely degrades the voice quality of the voice mail message. Some existing voice mail systems use automatic trunk test equipment to establish a test call between voice mail systems to determine the quality of the transmission medium before transmitting the voice mail message. Since the voice-grade trunks contain no error correction capability, this test call is one method of minimizing the loss of voice quality of the voice mail message.
The second factor is the cost of transmitting a voice mail message. This transmission cost is due to the fact that a voice mail message, generated on one voice mail service system and destined for a user served by another voice mail service system, must be transmitted along with header information over the transmission facilities that interconnect the plurality of message service systems. This transmission presently consists of the header and voice mail message in analog form, as received from the message originator. This voice mail message exchange consumes a significant amount of transmission capacity. For example, to provide the name of the message originator in the header requires approximately four seconds of speech which translates to 64K bits of PCM encoded data. To minimize the header information to reduce the transmission cost, the name of the message sender as well as the telephone number of the message sender is usually omitted from the voice mail message. The resultant transmission still occupies more time than the real-time transmission of the voice mail message. The exchange of a significant number of voice mail messages between two voice mail systems can apply a significant traffic load on the voice mail systems using such a message transmission arrangement.
These problems have presented a significant impediment to the networking of voice mail systems. As a result, existing voice mail networks provide poor quality voice transmissions at high cost.